Random Facts

Lots and lots of stuff, some useful (most probably not!). Lots of little 'hints' and tricks... esp. further down the page.

'Noise' in analogue circuits isn't always due to bad design, it's present because of the random-movement of electrons within the charged components (inc. wires). Noise can only be reduced by better design and can never be eliminated totally. Changing capacitance characteristics of wires can reduce the 'stored' charge, therefore free elctrons. So, cable choice, so-often laughed at by noiseboys can have a theoretical benefit, but you need to be trained in Quantum Physics to understand it.

RMS

The RMS value of an AC signal (I or V) is the equivalent DC value needed to deliver the same total power. ( RMS = PEAK*(1/root2) )

Dynamic Range

the 'range' between the quietist and loudest sounds in any given 'section'.

INTERMODULATION DISTORTION

Occurs in systems that are non-linear, ie: almost all to some degree.Complex, but, simply: if two frequencies are fed into the same system (say, a microphone), then the output contains small signals at the sum and difference of the two. Eg: Frequencies of 4kHz and 7kHz would have 'residual' signals at 3kHz and 11kHz. Why specification often contains a linearity rating.

Mix-Buss noise

can be present if a channel is routed to a master( the 1-2 and 3-4 type buttons), EVEN if that channel is muted; a minor point, but worth remembering if you're recording.

When trying to avoid an earth-loop, if you suspect an unbalanced piece of equipment is the source, check the resistance between the earth pin of the mains and the shield of the output, if it reads about 100Ohms (rather than 1 or 2) then the device has a built-in ground lift resistor, so isn't your problem.

A 31 Band EQ has 1/3 octave controls at these frequencies: 20, 25, 31.5, 40, 50, 63, 80, 100, 125, 160, 200, 250, 315, 400, 500, 630, 800, 1k, 1.25k, 1.6k, 2k, 2.5k, 3.15k, 4k, 5k, 6.3k, 8k, 10k, 12.5k, 16k, 20k. So now you know.

If you put a compressor/exciter on the master output, remember PUT IT ON PRE-FADE INSERTS; otherwise, the compressor will try to compensate when you fade the mix down: BAD.

XLR - Has pins 1,2 and 3, when connecting; 1=X="eXternal" (shield) and 2=L="Live" (hot, or +ve).

Peter J Baxandall

An early British electrical engineer who designed and built the first EQ ever; it was two channel and the design is still used in cheap hi-fi today.

The 'Stereo' Jacks used for inserts are called TRS (Tip Ring Sleeve); the Tip Transmits and the Ring Returns from the processor.

Normalising

In patch-bays, where the facility is given to insert an effect in a signal path, between two jack sockets, a 'normalised' socket set will, when no jack is inserted into either, connect the sockets together, to allow the signal to pass when no effect is patched-in. 

'Digital' clipping

occurs really quickly, as all the sample bits get used up and the supply of headroom STOPS dead. Whereas, analogue clipping is progressive.